The culturing of living cells in vitro is performed for a variety of purposes, including the preparation of viral vaccines, the recovery of by-products of cell metabolism, and the production of tissue or tissue-like derivatives for creating implants or artificial organs. Cell types that can be grown in culture can include connective tissue cells, skeletal cells, cardiac cells, epithelial cells, neural cells, endocrine cells, melanocytes, and many types of tumor cells. A variety of media are available, depending on the particular growth requirements of the cells and the growth conditions.
Typically, cell culture production of either cells or cell-secreted products begins with the small scale growth of cells. Traditional vessels for small volume cultures include multi-well plates, T-flasks, roller bottles and spinner flasks. In recent years a number of manufacturers have also begun to offer cell culture devices in the form of flexible, disposable bags formed of biologically inert and gas-permeable plastic materials such as fluoro-ethylene-propylene copolymers. Cell culture devices that involve the use of oxygen-permeable materials have also been used in recent years. For instance, a cell culture device can be constructed from a petri-dish that includes a base, which consists of a gas-permeable membrane, such as silicone rubber. Alternatively, a cell culture device can be constructed from a Roux bottle in which a side wall comprises the gas-permeable membrane.
Several problems are associated with growing cells in vitro to produce dense masses of cells. First, individual components of the nutrient medium must diffuse through the cell layers to reach all cells. This becomes increasingly difficult as the thickness of the cell layer increases. Second, the maintenance of a suitable environment for cell growth is difficult because the fluid immediately adjacent a growing cell is continuously changing as cellular metabolism proceeds and is returned to its original status only in stepwise fashion when the nutrient medium is changed or agitated en masse. Third, a lattice or suitable material upon which to grow some types of cells is often required.